In the event of an onground emergency aboard a large commercial passenger airplane which is away from the airport terminal boarding gate, emergency escape slides are typically used to evacuate the passengers and crew from the airplane cabin to the ground. These escape slides are stored inside the passenger doors of the airplane. Prior to normal operations for embarking and disembarking passengers at the airport terminal gate, the emergency escape slides are disarmed by the cabin flight attendants. This allows the cabin doors to be opened and closed in a normal manner without activating the emergency escape slides.
However, once the airplane leaves the airport terminal gate, the emergency escape slides are armed. Arming the emergency escape slides causes a metal girt bar attached to the girt at the upper end of each slide to be connected to the floor of the airplane cabin. In the event of a situation requiring emergency evacuation of the passengers from the airplane, current Federal Aviation Regulations require that each emergency escape slide be deployed by moving the door handle connected to the inside of the cabin door to the open position. This causes (i) the cabin door to open (on some airplanes the door must be manually pushed open), and (ii) the uninflated escape slide to fall from its storage pack inside the cabin door and to begin inflating outside the airplane. Since the upper end of the inflating escape slide is attached to the girt bar, the escape slide remains connected to the airplane.
During inflation, the escape slide has a tendency to pop open thereby resulting in a significant upward force being applied to the girt bar. This upward force can damage the girt bar thereby reducing its ability to effectively secure the slide to the airplane unless the girt bar is sufficiently heavy to withstand the vertical loads.